Flip-chip hybridization is currently used to assemble two microelectronic components manufactured independently from each other, but operating complementarily, such as for example an array of unit detection elements and its read circuit, more generally by forming electromechanical connections with solder bumps or by insertion of hard metal inserts in ductile metal pads.
Such hybridization is often completed by the filling of the space between the two hybridized components with a protection material, usually an epoxy resin, this operation being called underfilling.
The filling material indeed enables to absorb thermal expansion differences between the first and second electronic components, which generally do not have the same thermal expansion coefficient, to protect the interconnections between the two components from an adverse environment such as, for example, a humid environment, and to provide a mechanical protection against shocks and vibrations.
Although the filling material has many advantages, it cannot be applied to any type of hybridized component. Indeed, one of the components or both components may also have on their surface electronic circuits that cannot operate if they are embedded in the filling material. This is for example generally true for electronic chips, and in particular for light detection circuits, such as bolometric detectors or circuits of MEMS (Micro Electro Mechanical Systems) type, or again certain electric connections.
Further, some circuits specifically require a low pressure or vacuum to be able to operate, such as for example bolometric detectors which require an environment with a very low heat conductivity. In such cases, the underfilling operation according to the state of the art is then impossible, since it implies embedding said circuits.